1. Field of the Invention
The present invention relates to an ink jet recording head designed to perform recording by discharging a recording liquid (hereinafter referred to as xe2x80x9cinkxe2x80x9d) in the form of flying droplets from an ink discharge port and by directing the droplets onto a material to be recorded on, to which the droplets adhere.
2. Description of the Related Art
An ink jet recording apparatus uses a xe2x80x9cnon-impactxe2x80x9d recording method, and is advantageous in that it features high-speed recording and compatibility with a variety of types of recording media and is very quiet while recording. Because of these advantages, ink jet recording apparatuses are in extensive use as the recording mechanisms for printers, word processors, facsimiles, copying machines, etc.
A typical ink jet recording method employs electrothermal converting elements to cause minute droplets to be discharged from minute discharge ports so as to implement recording on a sheet of recording paper. The ink jet recording apparatus employing this method is generally constituted by an ink jet recording head for forming droplets and a system for supplying the ink to the head. The ink jet recording head using the electrothermal converting elements applies electrical pulses providing recording signals to the electrothermal converting elements installed in a pressurizing chamber so as to supply thermal energy to the recording liquid therein. This causes the recording liquid to change its phase, and bubble pressure is produced when the recording liquid bubbles or boils. The bubble pressure is utilized to discharge the recording liquid.
In recent years, there has been a demand for such an ink jet recording head to achieve a higher recording speed (a driving frequency of several dozen kHz). To meet the demand, a xe2x80x9cblock-based drivexe2x80x9d method has been known to be in use, in which the rows of nozzles are divided into blocks, and driving pulses for the same block are simultaneously sent to the electrothermal converting elements thereof.
However, if adjoining nozzles belong to different blocks, back waves generated when a first block bubbles may cause the adjoining nozzles to develop meniscus vibration. If driving pulses are sent to the electrothermal converting elements in the nozzles during meniscus vibration, the discharge will be adversely affected, with consequent unstable discharge direction or increased discharge mist. To solve such a problem, the interval between the blocks may be increased, and the driving may be started after the meniscus vibration ceases. This, however, has caused a drop in driving frequency.
Furthermore, when such block-based driving is performed, if different nozzle lengths are used to compensate for the differences in discharge timing, the distances from the electrothermal converting elements to the ink supply ports change and the flow resistances in the nozzles change accordingly, possibly causing the post-discharge ink refilling time to vary.
Meanwhile, a pillar-and-gap filter in a vicinity of a nozzle (hereinafter referred to simply as xe2x80x9ca nozzle filterxe2x80x9d) has been disclosed in Japanese Patent Laid-Open No. 05-124206, Japanese Patent Laid-Open No. 10-86377, etc. The pillar-and-gap filter is intended to prevent failure attributable to dust being mixed into a recording head during its manufacturing process or a recording head in use. However, achieving a higher recording speed requires improved efficiency of ink refilling after discharge, so that the flow resistance in a nozzle filter is required to be minimized. On the other hand, to block dust, the opening of the nozzle filter must be made smaller to minimize the amount of dust entering the nozzle. The conventional nozzle filters have not actually been very successful in meeting the conflicting requirements.
Accordingly, it is an object of the present invention to provide an ink jet recording head that solves the problems described above, and permits high-speed recording despite its simple construction.
To this end, according to the present invention, there is provided an ink jet recording head including a plurality of nozzles constituting a row of nozzles, a plurality of discharge ports for discharging ink, corresponding to the plurality of nozzles, the discharge ports communicating with the nozzles, respectively, energy generating devices for generating energy for discharging the ink from the discharge ports, and a common liquid compartment in communication with the plurality of nozzles constituting the row of nozzles, and further including a first filter provided at an end of at least one nozzle of the row of nozzles, the end being adjacent to the common liquid compartment, and a second filter that is provided at an end of a nozzle other than the nozzle provided with the first filter and that has a flow resistance lower than that of the first filter, this end also being adjacent to the common liquid compartment. To trap dust even more reliably, it is further preferred that at least one of two adjoining nozzles of a nozzle provided with the second filter is equipped with the first filter.
This arrangement makes it possible to satisfy two conflicting requirements, namely, the requirement for improved post-discharge ink refilling efficiency and the requirement for effectively trapping dust, which has not been achieved by conventional nozzle filters. More specifically, the delay in ink refilling can be improved by decreasing the flow resistance of the filter for a nozzle that is apt to cause delayed ink refilling because of its greater length. At the same time, however, the longer nozzle is provided with a filter to ensure reliable trapping of dust.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.